Wireless RFID networking systems and methods

ABSTRACT

Embodiments of the present invention include a wireless access point that acquires and processes radio frequency identification (RFID) information. The wireless access point may be coupled to a network of RFID readers over a wireless network. The RFID readers may read a plurality of RFID tags and transmit information to one or more readers. The readers may, in turn, transmit the RFID information to a wireless access point. The wireless access point may include a middleware layer for performing a variety of RFID data processing functions. In one embodiment, the wireless RFID reader network may be used to improve positioning of readers and tags, and may include a GPS system or position assisted GPS system at the reader and/or tag level.

BACKGROUND

The present invention relates to radio frequency identification(“RFID”), and in particular, to wireless RFID networking systems andmethods.

RFID systems are useful in a wide variety of applications. RFID systemsare radio communication systems that include small low cost electronicdevices that store information including identification (“ID”)information, for example. These devices are referred to as RFID tags.The RFID tags may be designed using backscattering circuit techniques,for example, so that another device can retrieve the ID wirelessly. Theretrieving device is typically referred to as a “reader,” and sometimes“an interrogator.” The tags are typically very small, and may be placedon a variety of items including equipment, products, or even people, forexample, and identification of such items may be made through a reader.Accordingly, RFID systems may be used to track inventory in a warehouse,the number of products on store shelves, or the location of equipment ina company, to name just a few example applications.

RFID systems may include large numbers of tags and readers spread outacross potentially wide areas. The large number of tags and readers mayresult in a correspondingly large volume of information that may need tobe processed. Such information may include large volumes of tag IDs. Inorder to process such information, powerful readers are typically usedthat include complex software capable of interfacing with backendsystems that store and ultimately use the data.

FIG. 1 is an example of a prior art RFID system. Information fromnumerous RFID tags 101A-C is received wirelessly by RFID readers 102A-C.Each RFID reader includes an RFID client software component 103A-C(e.g., a Savant Client) that is designed to operate with an RFID centralserver software component 110 (e.g., a Savant Server) over a network111. The central server 110 uses a client-server architecture for movingdata between the readers and the server. Since all the RFID specificoperations are included in two components, the readers are typicallypowerful systems that can work with the server to manage the dataretrieved from the RFID tags. The RFID central server, in turn, iscoupled to backend data storage and processing system 120 over network150. Backend system 120 may be coupled to a database 130 for storing theRFID data, for example.

It is generally desirable to reduce the cost of the tags and the readersthat access them. Additionally, it is desirable to improve themanagement of the RFID tags and the features and flexibility of the RFIDsystem. Existing RFID systems are expensive because, as mentioned above,readers require powerful processors to execute the client softwarerequired to interface with the server to make the system operational. Itwould be beneficial if a new architecture were developed to lower theoverall RFID system cost and improve the features and flexibility of theRFID system.

Thus, there is a need to improve RFID systems. Accordingly, the presentinvention provides improved wireless RFID networking systems andmethods.

SUMMARY

Embodiments of the present invention include a wireless access pointthat acquires and processes radio frequency identification (RFID)information. The wireless access point may be coupled to a network ofRFID readers over a wireless network. The RFID readers may read aplurality of RFID tags and transmit information to one or more readers.The readers may, in turn, transmit the RFID information to a wirelessaccess point. The wireless access point may include a middleware layerfor performing a variety of RFID data processing functions. In oneembodiment, the wireless RFID reader network may be used to improvepositioning of readers and tags, and may include a GPS system orposition assisted GPS system at the reader and/or tag level.

According to one embodiment of the present invention, a wireless accesspoint includes a first physical layer interface, a second physical layerinterface, and middleware software. The first physical layer interfacesthe wireless access point to a wireless link and communicates first RFIDdata to the wireless access point from a plurality of RFID readers. TheRFID readers read a plurality of RFID tags. The first RFID data resultsfrom reading the RFID tags. The second physical layer interfaces thewireless access point to a wired or wireless link and communicatessecond RFID data from the wireless access point to a server. Themiddleware controls the wireless access point to receive and store taginformation from the RFID tags. In this manner, the wireless accesspoint offloads processing from the server.

According to another embodiment of the present invention, the middlewarecontrols the wireless access point to process the tag information priorto transmission to the server.

According to yet another embodiment of the present invention, themiddleware controls the wireless access point to estimate a position ofa RFID tag.

According to still another embodiment of the present invention, themiddleware controls the wireless access point to pre-process globalpositioning system (GPS) information for an RFID reader.

These and other features of the present invention are detailed in thefollowing drawings and related description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of a prior art RFID system.

FIG. 2 illustrates an RFID network according to one embodiment of thepresent invention.

FIG. 3 illustrates an RFID network according to another embodiment ofthe present invention.

FIGS. 4A-F illustrate examples of RFID middleware on a wireless accesspoint according to other embodiments of the present invention.

FIG. 5 illustrates a network configuration according to one embodimentof the present invention.

FIG. 6 illustrates a network configuration according to anotherembodiment of the present invention.

FIG. 7 illustrates a network configuration according to anotherembodiment of the present invention.

FIG. 8 illustrates the position of tags within the coverage area of areader according to another embodiment of the present invention.

FIG. 9 illustrates the position of readers within the coverage area ofan access point according to another embodiment of the presentinvention.

FIG. 10 illustrates tag positioning according to another embodiment ofthe present invention.

FIG. 11A illustrates determining tag position according to anotherembodiment of the present invention.

FIG. 11B illustrates a method of determining tag position according toanother embodiment of the present invention.

FIG. 12 illustrates reader positioning according to another embodimentof the present invention.

FIG. 13A illustrates determining reader position according to anotherembodiment of the present invention.

FIG. 13B illustrates a method of determining reader position accordingto another embodiment of the present invention.

FIG. 14 illustrates an RFID network with integrated GPS according toanother embodiment of the present invention.

FIG. 15 illustrates an RFID network with integrated GPS according toanother embodiment of the present invention.

DETAILED DESCRIPTION

Described herein are techniques for networking RFID system components.In the following description, for purposes of explanation, numerousexamples and specific details are set forth in order to provide athorough understanding of the present invention. It will be evident,however, to one skilled in the art that the present invention as definedby the claims may include some or all of the features in these examplesalone or in combination with other features described below, and mayfurther include obvious modifications and equivalents of the featuresand concepts described herein.

FIG. 2 illustrates an RFID network according to one embodiment of thepresent invention. A plurality of RFID tags 201A-C may receive signalsfrom RFID readers 202A-C. The tags may be active or passivebackscattering circuits (i.e., with or without an internal source ofenergy such as a battery), for example, or in some embodiments a morecomplex sensor network capable of wireless automatic identification. Inresponse to the received signals, the RFID tags will transmitinformation back to the readers. Readers 202A may include a variety ofdevices such as application specific readers, personal digitalassistants, cell phones, or other handheld devices. RFID readers 202A-Care coupled together over a wireless network link 210 (i.e., acommunication channel). The wireless network link may be an 802.11wireless network link, a Bluetooth network link, a Zigbee network link,cellular network link, backscattering link, or other wireless networklink using radio frequency signals, for example. Thus, RFID reader 202Amay communicate with wireless access point 220A over a wireless network210. Similarly, RFID reader 202C may communicate with wireless accesspoint 220B over a similar wireless network 210. Accordingly, the readersand wireless access points include physical layer circuits and systemsfor implementing the wireless transmissions, such as RF transceivers andbaseband processors, for example. In some cases, an RFID reader may bewithin range of multiple access points. In this example, RFID reader202B is within range of both access points 220A and 220B. Accordingly,information from RFID reader 202B may communicate wirelessly with bothof access points 220A and/or 220B. In this example, wireless accesspoints 220A and 220B are coupled to a server computer 230 over a wired(e.g., Ethernet or RS-485) or wireless network 225. However, in someapplications the wireless access points may be coupled to a centralserver over a wireless network (in which case the central server may actas a central access point). The server computer 230 may, in turn, becoupled to backend applications and databases 260 over another network250, such as the Internet or an intranet, for example.

In one embodiment, an application layer is added to wireless accesspoints 220A-B. The application layer includes an access point middlewaresoftware component 221 that works with a middleware (“MW”) readersoftware component 203 to manage the network of RFID readers and relatedtags. In one embodiment, access point middleware 221A-B may be used fortag or reader registration, tag or reader positioning, or network anddata management. Access point middleware 221A-B may be used to hide thenetwork of RFID readers behind the access point thereby making thenetwork more flexible and reducing the processing burden on the server230. For example, in one embodiment, server computer 230 includes amiddleware host 231 that is part of a distributed middleware system forsimplifying management of the reader network. Server computer 230 mayfurther include an RFID central server 232 that communicates withwireless access points 220 and applications 233 for managing andprocessing data associated with the RFIDs. Additionally, Access pointsoftware 221A-B may be used to offload network management and dataprocessing from the reader, which lowers the cost of the reader, andaccordingly, the entire RFID network.

FIG. 3 illustrates an RFID network according to another embodiment ofthe present invention. A plurality of RFID tags 301A-D may receivesignals from RFID readers 302A-D. In response to the received signals,the RFID tags will transmit information back to the readers. RFIDreaders 302A-B are configured in a wireless network and communicate withwireless access point 320A over a wireless communication channel 310A,and RFID readers 302C-D are configured in a wireless network andcommunicate with wireless access point 320B over a wirelesscommunication channel 310B. Wireless access points 320A and 320B arecoupled to a server computer 330 over a wired or wireless network 325.RFID readers 302A-D include a middleware (“MW”) software component303A-D, and the wireless access points 320A-B include a middlewareapplication layer component 321A-B. In this example, the access points320A-B further include RFID client software components 322A-B.Embodiments of the present invention may move software functions fromthe reader to software executed on an application layer on the accesspoint. The RFID clients 322A-B perform transactions with an RFID centralserver software component 332 on server computer 330. Accordingly, thesoftware architecture in this example distributes RFID networkprocessing across the entire network to reduce the processing burden onthe reader and thereby reduce the overall cost of the network.

FIG. 4A illustrates an example of a network model for an RFID networkaccording to another embodiment of the present invention. This exampleshows the network model for a reader 410, access point 420, and servercomputer 430. The reader 410 and the access point 420 communicate over awireless network link 490. The access point 420 and the server computer420 communicate over a wired or wireless network link 491. The wired orwireless network link 491 may be, for example, a local area networkconnection such as Ethernet, an intranet, or a wide area network such asthe Internet, or any of the wireless networks described above.

The network model for reader 410 includes a physical layer, data linklayer, network layer, transport layer, and application layer. Theapplication layer may include a reader middleware software component(“Reader MW”) as described above. The physical layer in this case is awireless network link including a wireless receiver and transmittercoupled to an antenna.

Access point 420 includes a physical layer, data link layer, and networklayer. In one embodiment of the present invention, an access point 420is provided that further includes a transport layer and applicationlayer 421 for running access point middleware software 422 (“AP MW”)described above for preprocessing the RFID data. The physical layer mayinclude a wireless receiver and transmitter coupled to an antenna forcommunicating with one or more readers. The physical layer may alsosupport wired or wireless communication with another computer 430 (e.g.,Ethernet).

The AP MW 422 coordinates the input of RFID information 423 receivedfrom the reader 410, the storage of the RFID data in a storage unit 424,and the output of RFID information 425 to be sent to the server computer430. Such coordination includes functions such as monitoring andmanagement of the reader 410 (referred to as device management),connectivity management of the connection between the access point 420and the server 430, connectivity management of the connection betweenthe readers 410 and access point 420, fault detection of failures orother problems with the reader 410, maintenance and upgrades for thereader 410, and data management (processing) of RFID information. Suchdata processing may include data aggregation, data smoothing, datafiltering, redundancy processing, multiprotocol format negotiation (forexample, configuring the reader 410 to communicate with the RFID tagsusing different protocols, or responding to a request by the server 430to read all tags having a certain set of protocols). The access point420 may include a processor, controller, micro-controller, programmablelogic device, or other integrated circuit device that executes the AP MW422. The storage unit 424 may be a memory, hard disk, or other type ofstorage system.

Server computer 430 includes a physical layer, data link layer, networklayer, transport layer, and application layer. The application layer onthe server may include a central RFID server and other software forreceiving and processing RFID applications.

FIG. 4B illustrates a method according to another embodiment of thepresent invention. At 401, tag IDs are received in an application layerof a wireless access point on an input 423 of middleware 422. At 402,information associated with the tag IDs (e.g., position information) mayalso be received in middleware 422. At 403, the tag IDs are stored in arepository, such as a database or other data storage facility, forexample. At 404, the tag IDs and/or the associated information areprocessed by the middleware. As mentioned above, processing may includedata or device monitoring or management, for example. At 405, the tagIDs and/or the associated information are transmitted on middlewareoutput 425 over a wired or wireless link 491 to a server 430 for furtherprocessing if desired.

FIG. 4C illustrates an RFID network according to another embodiment ofthe present invention. A plurality of RFID tags 411 are located within alocation (such as a building or warehouse) that is covered by aplurality of RFID readers 410 (labeled R1, R2, R3 and R4). The RFID tags411 may receive signals from the RFID readers 410. In response to thereceived signals, the RFID tags 411 will transmit information back tothe readers 410. The RFID readers 410 are configured in a wirelessnetwork and communicate with a wireless access point 420 over a wirelesscommunication channel. The wireless access point 420 is coupled to aserver computer 430 over a wired or wireless network. The access point420 includes a MW software component (see above regarding FIG. 4A) thatin this case may be configured to offload redundancy processing from theserver 430, as discussed below with reference to FIG. 4D.

FIG. 4D illustrates redundancy offload processing according to anotherembodiment of the present invention. At 441, the wireless access point420 configures the readers 410 to cover a common location. Suchconfiguration may include sequencing the readers 410 for readingoperations (of the tags 411) or data transmission operations (to theaccess point 420) to manage the likelihood of interference. For example,the access point 420 may configure the reader R1 to read tags during afirst time segment, the reader R2 to read tags during a second timesegment, etc. As another example, the access point 420 may configure thereader R1 to transmit its information to the access point 420 during afirst time segment, the reader R2 to transmit its information during asecond time segment, etc. Alternatively, the access point 420 mayconfigure the readers 410 to communicate with tags and/or the accesspoint 420 at different frequencies. In yet other embodiments,communication between wireless access point 420, readers 410, and tagsmay be at different time slots and different frequencies. Readers 410may also use beamforming techniques and directional antennas tocommunicate with tags, for example, so different beams and/or differentpolarizations may also be used.

With reference to FIG. 4C, a particular RFID tag 411 may be in range ofmore than one of the readers 410. Including more than one reader 410allows for redundancy to improve reliability of the RFID system. Forexample, a particular RFID tag 411 may be blocked by shelving, etc. fromreceiving signals from the readers R1, R2 and R3, but may be situatedsuch that it receives signals from the reader R4. As another example, ifthe reader R1 fails, the other readers R2, R3 and R4 are stilloperational, allowing the RFID system to continue to function.

At 442, according to the particulars of the configuration (see 441above), the readers 410 receive the tag IDs from the tags 411 in thecommon area. At 443, according to the particulars of the configuration(see 441 above), the readers 410 transmit the tag IDs from each readerto the wireless access point 420. The access point 420 may store the tagIDs in the repository 424 (see FIG. 4A) along with an identifier thatidentifies which of the readers 410 read that tag. As multiple ones ofthe readers 410 may read the same tag 411, the storage unit 424 maycontain redundant tag data.

At 444, the access point 420 filters the redundant tag information. At445, the access point 420 sends the unique tag IDs to the server 430. Inthis manner, the access point 420 offloads redundancy processing fromthe server 430. The server 430 need not be aware of the specifics of theconfiguration of the readers 410.

FIG. 4E illustrates an RFID network according to another embodiment ofthe present invention. A plurality of RFID readers 410A, 410B and 410Cand a plurality of RFID tags 411A, 411B and 411C are located in an area.The readers 410A, 410B and 410C communicate with a wireless access point420 over a wireless communication channel. The readers 410A, 410B and410C have a range represented by “r” in the figure. Thus, tag 411B iswithin range of reader 410B, tag 411A is within range of reader 410A,and tag 411C is within range of both reader 410A and reader 410C. Thereaders 410A, 410B and 410C are separated by a distance, represented inthe figure by “d1” as the distance between the readers 410A and 410C,and by “d2” as the distance between the readers 410A and 410B. Theaccess point 420 includes a MW software component (see above regardingFIG. 4A) that in this case may be configured to offload read requestprocessing from the server 430, as discussed below with reference toFIG. 4F.

FIG. 4F illustrates read request offload processing according to anotherembodiment of the present invention. At 451, the access point 420determines the position of the readers within range of the access point.With reference to FIG. 4E as an example, the readers 410A, 410B and 410Care within range of the access point 420. The access point may use avariety of techniques for determining the position of the readers, asdiscussed below.

At 452, the access point 420 determines the distance(s) between thereaders. The access point 420 may determine the distances based on theposition information (see 451 above). With reference to FIG. 4E as anexample, the distance between the readers 410A and 410C is d1, and thedistance between the readers 410A and 410B is d2. According to oneembodiment, the distance between a particular reader and thenext-closest reader is relevant for the process of FIG. 4E, so thedistance between the readers 410B and 410C is not relevant for theprocess.

At 453, the access point 420 determines whether the distance betweenreaders (referred to as “d”) is greater than the range of the readers(referred to as “r”). If not, the access point 420 proceeds to 454; ifso, the access point proceeds to 455. With reference to FIG. 4E as anexample, the distance d1 between the readers 410A and 410C is notgreater than the range r (so proceed to 454); the distance d2 betweenthe readers 410A and 410B is greater than the range r (so proceed to455).

At 454, the access point 420 instructs the readers identified in 453 tosequence their read requests of the tags. In the case where d is notgreater than r, a particular tag may be within range of more than onereader. In such a case, by the access point 420 instructing the readersto perform read requests sequentially, a particular tag does not receivemore than one read request at the same time. With reference to FIG. 4Eas an example, the access point 420 instructs the readers 410A and 410Cto perform their read requests sequentially. When the reader 410Aperforms its read request, it reads tags 411A and 411C. When the reader410C performs its read request, it reads tag 411C. Sequenced readrequests avoid the tag 411C being read simultaneously.

At 455, the access point 420 instructs the readers identified in 453 toread tags in parallel. In the case where d is greater than r, there isno risk that a particular tag may be within range of more than onereader. Thus, the access point 420 may instruct the readers to performtheir read requests in parallel without a particular tag receiving morethan one read request at the same time. With reference to FIG. 4E as anexample, the access point 420 instructs the reader 410B to perform itsread requests in parallel with either the reader 410A or the reader410C.

Performing read requests in parallel increases the throughput of readingtags. Namely, if one reader can read N tags within a time period, Mreaders in parallel can read a number of tags equal to M*N in the sametime period. In the manner described above, the access point 420offloads read request configuration processing from the server 430 (seeFIG. 4A). The server 430 need not be aware of the specifics of theconfiguration of the readers 410A, 410B and 410C.

FIG. 5 illustrates a network configuration according to one embodimentof the present invention. Embodiments of the present invention may beimplemented using a variety of network configurations. In FIG. 5, RFIDreaders 510A-E communicate directly with wireless access points 520A-Bover a wireless network. In some cases, a reader may be within range ofa plurality of access points, such as reader 510C, and may communicatedirectly with multiple access points. The wireless access points 520A-B,in turn, communicate with a server computer 530 over a wired or wirelessconnection. FIG. 6 illustrates a network configuration according toanother embodiment of the present invention. In this example, aplurality of readers 610A-F may communicate wirelessly with the wirelessaccess point through a local network coordinator reader 610G. Reader610G may connect to access point 620 for providing all reader networktraffic over a wireless communication channel. Wireless access point620, in turn, communicates with server computer 630. The configurationof RFID readers in FIG. 6 is referred to as a “star” network. FIG. 7illustrates a network configuration according to another embodiment ofthe present invention. In this example, all readers 710A-G includerouter components and can communicate directly with all other readers.One reader 710G may act as the local network coordinator forcommunicating with wireless access point 720. The configuration ofreaders 710A, 710B, 710D, 710F, and 710G is referred to as a “completemesh” network. Various modifications on the above configurations arepossible, including hybrid networks. In this example, readers 710C and710E communicate through readers 710B and 710D, respectively, whichresults in a hybrid network.

FIG. 8 illustrates the position of tags within the coverage area of areader according to another embodiment of the present invention. Therange of an RFID reader 810 is illustrated in FIG. 8. Different RFIDreaders may have different ranges depending on the particulartechnologies selected to implement the system. The maximum range atwhich a reader can send out a signal and receive a response from an RFIDtag is depicted by R1. Tags 801A-D within this range will receive asignal from the reader and provide a response signal to the reader. Thedistance between reader 810 and tag 801E is greater than R1. Therefore,tag 801E may not receive a sufficiently large signal to provide aresponse, or the response signal may be too small to be detected byreader 801E. In either case, tag 801E is outside the coverage area ofreader 810 and will not be detected.

FIG. 9 illustrates the position of readers within the coverage area ofan access point according to another embodiment of the presentinvention. The range of an access point 920 is illustrated in FIG. 9.Different access point-reader combinations may have different rangesdepending on the particular wireless communication technologies selectedto implement the system. The maximum range at which an access point canestablish a wireless communication with an RFID reader is depicted byR2. Readers 910A-D are within range, and accordingly may establish acommunication link to the access point 920. The distance between accesspoint 920 and reader 910E is greater than R2. Therefore, reader 910E maynot communicate with access point 902. Accordingly, reader 910E isoutside the coverage area of access point 920.

FIG. 10 illustrates tag positioning according to another embodiment ofthe present invention. When a tag is within a reader's coverage area,information stored on the tag and transmitted to the reader in responseto a read request may be processed by software on the reader, the accesspoint, or both. To initiate the process, a reader sends out a readrequest signal and the tag responds by transmitting tag information. At1001, the reader receives the tag information (e.g., tag IDs). At 1002,the tag information is stored locally on the reader. In one embodiment,the reader may include a local database for storing tag information, forexample.

Features of the present invention include determining the position oftags. Accordingly, at 1003 an initial position of the tag is determined.For example, in one embodiment the tag position may be determined towithin the range of the reader based on the position of the reader(e.g., if the position of the reader is known). In particular, somereaders may reside in known fixed locations. The location may beprogrammed into the reader, for example, and used to identify theposition of the tag (e.g., if a reader with a range of 25 ft is locatedin the North corner of a warehouse at a certain address, then any tagdetected by the reader is within 25 ft of that location). In otherembodiments described in more detail below, tag positions may bedetermined more accurately from the power of the tag signal received inthe reader, the angle of reception, the time of arrival, the timedifference of arrival (e.g., between multiple readers as discussedbelow), a carrier phase measurement, triangulation with other readers,or through a global positioning system (“GPS”). In one embodiment,differential measurement techniques may be used to more accuratelydetermine tag positions. For example, If one tag is within range of tworeaders, the power, angle, time of arrival and carrier phase may bemeasured by both readers, and middleware in the access point may be usedto more accurately calculate the tag position relative to each reader.Similarly, if two tags are read by one reader, differential calculationsmay be applied. In one embodiment, multiple tags read by at least tworeaders may be read, and the middleware may calculate measureddifferences between tags in each reader and again between differentreaders to obtain a double difference calculation of the parameter ofinterest, thereby improving the position calculation even more.

At 1004, received tag IDs are entered into a local tag location registerin the reader. In one embodiment, the tag IDs are transmitted to theaccess point at 1005. The tag IDs may be entered into a global taglocation register on the access point, for example, at 1006. In someembodiments, an RFID system may include readers with overlappingcoverage areas. Accordingly, a tag may respond to multiple readers. If atag responds to multiple readers, the tag ID may be entered into a localtag location register on a plurality of readers. Additionally, if eachreader is communicating wirelessly with the same access point, the tagID and an identification of each reader (i.e., a reader ID) will be sentto the access point. The access point may store the tag ID multipletimes—once for each reader—together with each reader's ID.

In some applications, the tag is attached to an object that may movefrom one location to another. Alternatively, the tags may be in fixedlocations and the readers move from one location to another.Accordingly, at 1007, tags may move from one reader's coverage area toanother reader's coverage area. At 1008, tags that leave a coverage areaare de-registered from the local tag location register. At 1009, theglobal tag location register is updated. Accordingly, tags that haveleft the coverage area are de-registered and tags that enter thecoverage area are registered. In one embodiment, tag registration may beupdated with each read cycle initiated by a reader, for example.

FIG. 11A illustrates determining tag position according to anotherembodiment of the present invention. As mentioned above, a tag may bedetected by more than one reader. For example, as shown in FIG. 11A, atag 1140 is within the coverage area of three (3) readers 1110, 1120,and 1130. A method of determining tag position according to anotherembodiment of the present invention is shown in FIG. 11B. At 1101, thetag ID is received on multiple readers. If each reader's position isknown, then the position of the tag may be estimated based on the readerpositions. For example, if the positions of reader 1110 and 1120 areknown, then the distances between these positions may be calculated.Additionally, if the range of each reader is known, then the region ofoverlapping coverage may also be determined. If a tag is detected bymultiple readers, the position of the tag can be estimated to within theregion of overlapping coverage. In other embodiments, the range of thetag from each reader may be estimated by the power of the tag signalreceived in the reader, the angle of reception, the time of arrival, thetime difference of arrival, and carrier phase as mentioned above. At1102, the ranges from the tag to each reader are determined. At 1103,the ranges are transmitted to an access point. At 1104, locationsoftware may be used to estimate the position of the tag from datareceived from each reader. This may include calculating overlappingregions, determining ranges, or performing triangulation based on threetag-to-reader ranges to improve the accuracy of the tag position. In oneembodiment, optimization techniques, such as least squares estimates maybe used to further improve the tag position accuracy.

At 1105, the tag position is stored in a global tag location register(“GTLR”) on the access point. At 1106, the tag position may betransmitted back to each reader over the wireless channel. At 1107, thetag position may be stored in local tag location registers (“LTLR”) foreach reader. Tag position updates may be performed under the control ofeach reader or under the control of the access point. Tag positionupdates may occur periodically at predetermined intervals, after eachread cycle, or in response to user commands or other events (e.g.,automatically when a reader comes within the coverage area of a newaccess point). For example, in one embodiment, when an access pointdetects that a new reader has entered its coverage area, the accesspoint may send commands to the new reader or all readers in the area toscan for tags in each reader's coverage area specifically for a positionupdate. After new tag information is received by each reader, tagpositions may be determined and the information may be updated on theaccess point or readers or both (e.g., in the GTLR or LTLR).

FIG. 12 illustrates reader positioning according to another embodimentof the present invention. In some embodiments, readers may be moved fromone location to another, or the readers may be integrated on mobiledevices such as personal digital assistants (“PDA”), cell phones, or anyother handheld electronic device. If the readers are movable, then areader may move between coverage areas of different access points.Embodiments of the present invention may track reader positionsdynamically to improve RFID system performance. At 1201, a reader mayenter the coverage area of an access point. At 1202, the readerregisters with the access point. At 1203, the initial reader position isdetermined based on the known position of the access point. At 1204, thereader ID is entered into a local reader location register (“LRLR”) inthe access point. At 1205, the reader ID is transmitted to a servercomputer system, which may be coupled to multiple access points, forexample. Embodiments of the present invention include coupling a remoteserver to the access point over a computer network, such as the Internetor an intranet. At 1206, the reader ID is entered into a global readerlocation register (“GRLR”) on the server. At 1207, the reader may movefrom one access point coverage area to another. At 1208, the reader isde-registered from the LRLR on the access point. At 1209, the GRLR onthe server is updated to reflect that the reader is no longer in theaccess point's area.

FIG. 13A illustrates determining reader position according to anotherembodiment of the present invention. As mentioned above, a reader may bedetected by more than one access point. For example, as shown in FIG.13A, a reader 1340 is within the coverage area of three (3) accesspoints 1310, 1320, and 1330. A method of determining reader positionaccording to one embodiment of the present invention is shown in FIG.13B. At 1301, the reader ID is received on multiple access points. Ifeach access point's position is known, then the position of the readermay be estimated based on the access point positions. For example, ifthe positions of access points 1310 and 1320 are known, then thedistances between these positions may be calculated. Additionally, ifthe range of each access point is known, then the region of overlappingcoverage may also be determined. If a reader is detected by multipleaccess points, the position of the reader can be estimated to within theregion of overlapping coverage. In other embodiments, the range of thereader from each access point may be estimated. At 1302, the ranges fromthe reader to each access point are determined. At 1303, the ranges aretransmitted to a server. At 1304, location software may be used toestimate the position of the reader from data received from each accesspoint. This may include calculating overlapping regions, determiningranges, or performing triangulation based on three differentreader-to-access point ranges to improve the accuracy of the readerposition. In one embodiment, optimization techniques, such as leastsquares error minimization of the distance estimates, may be used tofurther improve the triangulation results and the reader positionaccuracy.

At 1305, the reader position is stored in a global reader locationregister (“GRLR”) on the server. At 1306, the reader position may betransmitted back to each access point over the wired or wirelessnetwork. At 1307, the reader position may be stored in local readerlocation registers (“LRLR”) for each access point. Reader positionupdates may be performed under the control of each access point or underthe control of the server. Reader position updates may occurperiodically at predetermined intervals, after each read cycle, or inresponse to user commands or other events (e.g., automatically when areader enters or leaves the coverage area of an access point). Forexample, in one embodiment, when an access point detects that a newreader has entered its coverage area, it may send a signal to the serverto trigger all access points to perform a scan for readers in each areaspecifically for a position update. After new reader information isreceived by each access point, reader positions may be determined andthe information may be updated on the server or access points or both(e.g., in the GRLR or LRLR).

FIG. 14 illustrates an RFID network with integrated GPS according toanother embodiment of the present invention. In some embodiments, thetags 1401, readers 1402, or access points 1420 may include limited orfull GPS functionality, and the wireless RFID reader network may be usedto improve positioning of readers and tags using the GPS system orassisted GPS system at the reader level (i.e., between the access pointand reader) or at the tag level (i.e., between the reader and the tag).For example, access points 1420 may have full GPS systems 1422integrated into the access point, readers may have no GPS, partial GPSor full GPS integrated into the reader, and tags may have no GPS,partial GPS or full GPS integrated into the tag. In one embodiment, afull GPS receiver is included in one or more access points 1420A-B andthe GPS receiver included in each reader 1402A-C may support anycombination of three modes, namely, autonomous mode, reader-based mode,and reader-assisted mode. Access point GPS 1422 tracks signals fromsatellites to determine the position of the access point. In theautonomous mode, the reader also includes a full GPS receiver, which isused to track all or a number of the visible satellite signals andcalculate the reader position and possibly velocity internally in thereader. In reader-based mode or reader-assisted modes, the position andsatellite information from the access point are used to improve thespeed and accuracy in determining the reader locations. The reader mayreceive information as to which satellites to track. The readers may beprovided with a smaller range of code and frequency offsets to search,thereby reducing the GPS acquisition time for the reader and enablingthe GPS acquisition for the reader in regions with lower received GPSsignal SNR. The readers may also receive GPS navigation data to enablethe GPS receiver 1403A-C embedded in readers 1402A-C to increase thecoherent correlation interval as described below, and thereby trackweaker GPS signals (i.e., improving sensitivity). In the reader-basedmode, the reader obtains the assisting data from the access point andtracks all or a number of visible satellite signals to obtain the GPSraw measurements (any combination of pseudoranges, pseudodopplers, andaccumulated carrier phase) and to calculate the reader position andpossibly velocity internally in the reader. In reader-assisted mode, onthe other hand, the final reader position and/or velocity are calculatedinside the access point and not in the reader. Specifically, the readeruses the assisting data from the access point to improve its signalacquisition and tracking performance and to obtain the GPS rawmeasurements or just the GPS signal correlations. The GPS rawmeasurements or GPS correlation outputs are then transmitted back to theaccess point where the reader position and/or velocity are calculatedwhich may then be communicated back to the reader.

For example, in one embodiment, the GPS in the access point may use atracking loop and a correlation scheme to track the signals fromdifferent satellites. However, the process of tracking and correlatingdata in a GPS can be computationally intensive. In one embodiment, theaccess point transmits the tracking information to the reader over thewireless communication channel so that the reader can track satellitesfaster and with reduced processing. For example, the access point maycorrelate data signals from satellites with a locally generatedpseudo-random (“PN”) code (e.g., a high speed pulse train) in order totrack each satellite. If the GPS signal comprises 50 Hz data modulatedinto a 1 MHz spread spectrum code, then the correlation length cannot bemore than 20 ms (1/50 Hz) or the data will change and the correlationmay become destructive. However, since the access point is decoding andcorrelating the GPS data, the access point may pass on this informationto the reader over the wireless network so that the reader will not berequired to decode the data from the satellite. This allows the readerto correlate over longer time periods (i.e., greater than 20 ms),thereby improving the processing gain, allowing averaging to occur overa longer period of time, and thereby allowing the reader to track weakersignals. After the reader receives the GPS information from the accesspoint, it performs the correlation as described above to obtain the GPSraw measurements. The reader then may use the GPS raw measurements toobtain the reader position and/or velocity internally (reader-based) ormay communicate the GPS raw measurements to the access point where thereader position and/or velocity are calculated (reader-assisted).

In another embodiment, GPS information transmitted to readers 1402A-Cmay be further transmitted to tags 1401. FIG. 15 illustrates anotherembodiment of the present invention. In this example, each tag 1501includes limited GPS functionality (e.g., a correlation engine). Accesspoint GPS 1507 tracks signals from satellites to determine the positionof the access point. The position and satellite information from theaccess point may be used to improve the speed and accuracy indetermining both the reader locations and the tag location. Similar toreader-access point GPS related interactions, the embedded GPSfunctionality in the tags may support autonomous, tag- based, andtag-assisted modes. In autonomous mode, a full GPS receiverfunctionality should be embedded in the tags. For tag-based mode, thetags still have a full GPS receiver embedded in them, except that theycan also get the assisting data from the reader to improve their GPSsignal acquisition and tracking. In tag-assisted mode, the tags onlyhave a limited functionality GPS receiver such as a correlation engineembedded in them to only obtain the GPS raw measurements or possiblyjust the correlation results and communicate them back with the readerwhere the tag position and/or velocity are calculated. The tag mayreceive information from the reader as to which satellites to track. Thetags may be provided with a smaller range of code and frequency offsetsto search, thereby reducing the GPS acquisition time for the tag andenabling the GPS acquisition for the tag in regions with lower receivedGPS signal SNR. The tags may also receive GPS navigation data to enablethe GPS receiver 1502 embedded in tag 1501 to increase the coherentcorrelation interval as described above, and thereby track weaker GPSsignals (i.e., improving sensitivity). In some embodiments, each reader1503 may have a full GPS system to interact directly with the tag'slimited GPS system 1502.

The above description illustrates various embodiments of the presentinvention along with examples of how aspects of the present inventionmay be implemented. The above examples and embodiments should not bedeemed to be the only embodiments, and are presented to illustrate theflexibility and advantages of the present invention as defined by thefollowing claims. Based on the above disclosure and the followingclaims, other arrangements, embodiments, implementations and equivalentswill be evident to those skilled in the art and may be employed withoutdeparting from the spirit and scope of the invention as defined by theclaims. The terms and expressions that have been employed here are usedto describe the various embodiments and examples. These terms andexpressions are not to be construed as excluding equivalents of thefeatures shown and described, or portions thereof, it being recognizedthat various modifications are possible within the scope of the appendedclaims.

1. A method for managing a set of tag readers by an access point, the access point having a coverage area for monitoring the set of tag readers, each tag reader having a coverage area for monitoring a set of tags, the method comprising: determining groups of tag readers, wherein each tag reader within a group has a coverage area that overlaps coverage areas of other tag readers in the group and tag readers from different groups do not have coverage areas that overlap each other, wherein said determination is based on (i) a range of the coverage area of each tag reader and (ii) a distance between each particular tag reader and a closest tag reader to the particular tag reader; for each particular group, configuring all tag readers within the particular group to sequentially transmit read requests to the set of tags in the coverage area of each tag reader in order to prevent simultaneous read requests being sent to a particular tag that is positioned in overlapping coverage areas of at least two tag readers; and configuring a plurality of tag readers that do not belong to a same group to transmit read requests in parallel.
 2. The method of claim 1 further comprising determining the distance between each particular tag reader and the closest tag reader to the particular tag reader based on a known fixed location of at least one reader.
 3. The method of claim 1 further comprising determining the distance between each particular tag reader and the closest tag reader to the particular tag reader by determining a location of one or more tag readers that reside in overlapping coverage areas of the access point and at least one other access point.
 4. The method of claim 1 further comprising determining the distance between each particular tag reader and the closest tag reader to the particular tag reader using a Global Positions System (GPS) module in at least one tag reader.
 5. The method of claim 1, wherein the set of tags are Radio Frequency Identification (RFID) tags and the set of tag readers are RFID readers, the RFID tags comprising backscattering circuits for communicating with the RFID readers.
 6. The method of claim 1, wherein the set of tag readers and the set of tags are communicatively coupled through a wireless sensor network.
 7. The method of claim 1, wherein each tag reader is one of an application specific reader, a personal digital assistant, and a cell phone.
 8. The method of claim 1, wherein the set of tags is configured as a sensor network, wherein tags in the set of tags provide automatic identification to the set of tag readers through a wireless link.
 9. An access point for managing a set of tag readers, the access point having a coverage area for monitoring the set of tag readers, each tag reader having a coverage area for monitoring a set of tags, the access point comprising: an interface for communicating with the set of tag readers; and a module (i) to determine groups of tag readers, wherein each tag reader in a group has a coverage area that overlaps coverage areas of other tag readers in the group and tag readers from different groups do not have coverage areas that overlap each other, wherein said determination is based on a range of the coverage area of each tag reader and a distance between each particular tag reader and a closest tag reader to the particular tag reader, (ii) to configure all tag readers within each particular group to sequentially transmit read requests to the set of tags in the coverage area of each tag reader in order to prevent simultaneous read requests being sent to a particular tag that is positioned in overlapping coverage areas of at least two tag readers, and (iii) to configure a plurality of tag readers that do not belong to a same group to transmit read requests in parallel.
 10. The access point of claim 9, wherein the module further determines the distance between each particular tag reader and the closest tag reader to the particular tag reader by determining a location of one or more tag readers that reside in overlapping coverage areas of the access point and at least one other access point.
 11. A system for managing a set of tag readers, the system comprising: a set of tags, each tag in the set communicatively coupled to at least one tag reader; the set of tag readers communicatively coupled to an access point, wherein the set of tag readers receive read requests from the access point and transmit the read requests to the set of tags; and the access point having a coverage area for monitoring the set of tag readers, wherein the access point determines groups of tag readers, each tag reader in a group having a coverage area that overlaps coverage areas of other tag readers in the group and tag readers from different groups do not have coverage areas that overlap each other, said determination based on (i) a range of the coverage area of each tag reader and (ii) a distance between each particular tag reader and a closest tag reader to the particular tag reader, wherein the access point configures all tag readers within each particular group to sequentially transmit read requests to the set of tags in the coverage area of each tag reader in order to prevent simultaneous read requests being sent to a particular tag that is positioned in overlapping coverage areas of at least two tag readers, and wherein the access point configures a plurality of tag readers that do not belong to a same group to transmit read requests in parallel.
 12. The system of claim 11, wherein the access point communicates with the set of tag readers via a wireless communication channel.
 13. The system of claim 11, wherein each of the set of tag readers comprises a Global Positions System (GPS) module, wherein the access point further determines the distance between each particular tag reader and the closest tag reader to the particular tag reader by using information transmitted from the GPS modules in the tag readers. 